Tyrosine kinase is an enzyme that transfers a phosphate group from ATP to a protein, resulting in attachment of the phosphate group to a tyrosine in the protein.
Phosphorylation of a tyrosine in a protein provides a mechanism via which cellular oncogenes deregulate various signaling pathways and thereby induce transformation. Tyrosine kinase is therefore an important target for anticancer therapy. See Van der Geer, P., Hunter, T. and Lindberg, R. A. Annu. Rev. Cell Biol., 1994, 10, 251; Levitzki, A. and Gazit, A. Science, 1995, 267, 1782; and Marshall, C. J. Cell, 1995, 80, 179.